[deprecate] old useful items following successful live production of new useful process

[iSCJT]

Following successful promotion of #2344 to live deployments certain deprecated items can be removed from the platform:

• user.models.tsx
  votedUsefulHowTos property
  votedUsefulResearch property

• aggregations.store.tsx
  remove users_votedUsefulHowtos & users_votedUsefulResearch from AGGREGATION_DOC_IDS

• user.store.ts
  remove actions updateUsefulHowTos & updateUsefulResearch

• Howto.tsx
  remove userStore declaration and userStore.updateUsefulHowTos() call

• ResearchArticle.tsx
  remove commonStores import, userStore declaration and userStore.updateUsefulResearch() call